1. Field of the Invention
This invention relates to the field of noise suppression in mechanical equipment and more particularly pertains to noise suppression in gearing, especially backlash noise in automotive manual transmission gearing.
2. Description of the Prior Art
When the engine of a motor vehicle is idling and the neutral clutch that connects the engine to a manual transmission is disengaged, the speed of the engine varies as a result of the cyclic irregularity that is intrinsic in the operation of an internal combustion engine. Countershaft manual transmissions for automotive use contain gearsets whose members are in continuous meshing engagement, though the gear selector of the transmission be in the neutral position. When the neutral clutch is engaged and the gear selector is in the neutral position, the speed changes of the engine, transmitted to the gearset, produce noise called gear rattle. When the engaged gear teeth change position with respect to each other due to the engine speed variations, the teeth of the driven gear contact alternately the driving face and the non-driving face of the driving pinion.
In order to reduce or eliminate the objectionable noise that results from this contact, various devices have been employed to take up the clearance between the faces of the gear and the pinion. Such devices include a wheel coaxial with the gear having similar teeth to those of the gear and means for elastically maintaining the teeth of the wheel in a position that is angularly offset relative to the gear. Usually a mechanical spring, such as a helical spring located radially offset from the axis of the gear, applies a force, directed tangentially to the axis, tending to rotate the annular element with respect to the gear wheel. Examples of devices of this type are described in the following U.S. Pat. Nos. 1,435,571; 1,748,820; 1,750,679; 2,607,238; 3,365,973; 3,496,794; 3,535,948; 3,648,534 and 3,803,936.
The prior art described resilient means other than a mechanical spring for biasing the annular member angularly with respect to the gear. But the uniformity of the springs and their equivalents, their loading and the degree of tooth displacement between the toothed wheel and the gear is difficult to control. In the combination of a gear and wheel with springs under compression or tension it is difficult to assembly and control the preload uniformly. Furthermore, spring preloaded gears require generally a widely spaced gear arrangement, whereas anti-backlash gearing in a narrow space is usually required in a narrow space. The teeth of the gear and the teeth of the wheel are first angularly offset and then the gear and wheel are mechanically connected by a soft resilient elastic member such as a pin or rivet made from rubber or another elastomer. Later when the gear is assembled in a transmission, the wheel is rotated with respect to the gear until their teeth are more nearly aligned sufficiently to mesh with the teeth of a pinion with which the gear transmits power. The resilient member maintains a biasing force between the wheel and the pinion which prevents backlash. Examples of this arrangement are described in U.S. Pat. Nos. 2,845,809; 3,127,784 and 3,318,193.